Professor Kirkwood: 'It's a myth that they are bowls of misery, unhappy with their lot, and always going on about ailments.' Photograph: Christopher Thomond for the Guardian

Professor Tom Kirkwood has demolished a string of misconceptions about the ageing process with a groundbreaking study into the health of more than 1,000 older people in the 85-plus generation. "It's a myth that they are bowls of misery, unhappy with their lot, and always going on about ailments," he insists. "Four out of five of them actually think they are doing pretty well."

His study, the largest of its kind ever undertaken, has proved revealing on several fronts. For a start, people in the 85-plus range are generally much happier, and more independent, than is generally realised. Remarkably, 80% of a group carefully selected by the Kirkwood team – a fair sample of the UK population of this age – need little care. Around the same number rate their quality of life either good or excellent.

On the downside, 20% need either regular daily help or critical 24-hour care. All of which might be almost manageable for the state, and for society, if this age range was static. But, as the amiable Kirkwood never tires of reminding questioners, the 85-plus group is now the fastest-growing segment of the population.

While the most recent analysis showed that the number of people in the UK aged over 80 to be at 2.6 million, by 2030 the figure is likely to jump to 4.8 million – and one in five will need regular care. Kirkwood's team, at the world-leading Biomedical Research Centre in Ageing at Newcastle University, estimates that this will lead to an 82% increase in the demand for places in care homes, with an additional 630,000 older people needing accommodation.

This prompted one of Kirkwood's academic colleagues to gently remind the government last year that it needs to be investing in elderly care and research to learn more about "healthy ageing". Ministerial inaction over the Dilnot commission's recommendation for capping the cost of care at £35,000 per person has emphasised his point.

Tracking activities

Kirkwood's project is comprehensively tracking the activities, and wellbeing, of people once considered very old. Known as the Newcastle 85+ Study, it began in 2006 when more than 1,000 85-year-olds, from Newcastle upon Tyne and North Tyneside, were carefully selected from all social classes and backgrounds through GP practices. Most agreed to full, "multidimensional assessments" by a team of research nurses, including cognitive abilities, body measurements and blood tests. Beginning with a baseline appraisal, it initially involved follow-ups at 18 and 36 months using laptops, and games – much preferred to paper and pen by the participants.

Why this age group? "Although the 85-plus population is the fastest growing, it's quite extraordinary how little we know about what 85-plus-year-olds are like," says Kirkwood, a fairly youthful 60-year-old. "We've known for some time that ageing is extremely variable; that everybody is different and that the differences of individuals' experience of ageing are greater than differences in earlier stages of life."

And why so variable? "Because of the nature of the ageing process. I've been involved in this field for more than 35 years and when I entered it people fondly believed that ageing was programmed; that there was a mechanism inside our bodies that determined how long we would live. It was kind of written into our genes that we would die at a certain age. What we've been able to show is that the idea of this genetically programmed ageing makes no sense at all. There is no evidence."

But, surely, genetic influences – a family susceptibility to cardiovascular problems, for instance – play a part in determining longevity? Only to a degree, insists Kirkwood. He points to a Danish study showing that such influences only explain about a quarter of the factors determining a lifespan.

Kirkwood explains: "What we now know is that the genetic factors that influence your longevity are not genes that measure out the passage of time; the reason we age and die is because, as we live our lives, our bodies accumululate a great variety of small faults in the cells, and the molecules that make up the cells in our body – so ageing is driven by this accumulation of faults. The genes that influence longevity are those that influence how well the body copes with damage, how aggressive our repair mechanisms are; they're genes that regulate the house-keeping and maintenance and repair."

And while some are endowed with these genes, others are not so fortunate, although Kirkwood is quick to point out that healthy lifestyle choices – good nutrition and moderate exercise, for instance – clearly play their part in determining longevity.

Kirkwood, a former BBC Reith lecturer, has been fascinated by the ageing process for much of his professional life. He fondly remembers a get-together with many of the participants in the study, now aged 91. "It was such a wonderful day," he recalls. "They were the sparkiest, most engaged individuals you could imagine." This reinforced his view that a large proportion of the elderly population was enjoying a pretty good and healthy quality of life."

But sadly, he accepts, disadvantaged groups are not always so fortunate. He produces a graphic on his PC, an adaptation of the Tyne and Wear metro map, showing a big variation in the age at which people get a long-term medical condition – linked to the areas around stations. Those living near a station in a poorer part of Newcastle (Byker) on average contract an ailment at 64 – 11 years before others only a few miles away near the wealthier suburb of Ponteland. "Life expectancy would be the same ratio," he laments. "If we could bring health and life expectancy of disadvantaged groups up to the level of the affluent, we would jump dramatically up the [longevity] league table."

Perhaps to his amazement, official longevity forecasts have proved wide off the mark. Until relatively recently, he recalls, all the best brains in the world were forecasting that life expectancy would stall. "UN forecasts of 1980 predicted it was going to bump into a ceiling and stop increasing next week, but it didn't happen; [it] carried on increasing pretty much as before."

Why? "Something profound had changed ... we were reducing the deaths in the early and middle years of life; we were reducing deaths around people who were very old – 80 and over – and those rates are [now] less than half what they were in 1951, the year I was born. This presents a really important challenge: to understand what life is like for the growing numbers of older people. We really want to understand something about the factors that influence the personal trajectory of health into old age."

Cost of caring

Of course, this has huge implications for the cost of caring. Revealingly, in tracking 17 activities of daily living among survey participants – from dealing with finances to cooking and shopping – researchers found that men fared better than women; a third managed all 17 without help, compared with a sixth of women. Although women live, on average, five to six years longer than men, the study has found that their disabilities become greater with age.

As it stands, Kirkwood thinks we should all take comfort in life expectancy increasing by about two years every decade. He delights in translating this into a daily cycle. "In the UK, it is going to increase by about five to six hours, so most of us get out of bed fondly imagining we are waking up to a 24-hour day, when in reality it's a 29-hour day." Phew!

Curriculum vitae

Career 2011-present: dean for ageing, Newcastle University; 2004-11: director, Newcastle University Institute for Ageing and Health; 1999-2004: professor of medicine, Newcastle University; 1993-99: professor of gerontology, University of Manchester; 1981-93: head of the laboratory of mathematical biology, National Institute for Medical Research; 1973-81: staff scientist, National Institute for Biological Standards and Control.

Interests Smallholding, rearing poultry.

• Tom Kirkwood is dean for ageing at Newcastle University's Institute for Ageing and Health, which supports the recently transferred gallery exhibition Coming of Age: the Art and Science of Ageing, 1 June-18 August, GV Art, London, www.gvart.co.uk. He will be participating in The Long Run: Life is a Marathon, a public discussion on ageing and vitality at the Royal Society of Arts, London, 12 July. www.theRSA.org/events.

• This article was amended on 1 June 2012 to clarify the location of Magdalen College school.